1. Why Radon Units Matter
Radon is a radioactive gas, and its concentration in air is measured by how much radioactive decay is happening in a given volume. The two main units used worldwide, pCi/L and Bq/m³, both measure the same thing: the rate of radioactive disintegration per unit volume of air.
Understanding these units matters because your test result is just a number until you know what it means. When your test comes back at 3.8 pCi/L, you need to know whether that is cause for concern (it is near the EPA action level of 4.0). When an international study references 200 Bq/m³, you need to know that is equivalent to about 5.4 pCi/L to put it in context with US guidelines.
If you are reading about radon online, you will encounter both units depending on whether the source is American or international. Knowing how to convert between them helps you understand radon information from any source.
2. Picocuries per Liter (pCi/L)
The picocurie per liter is the standard radon measurement unit in the United States. Here is what it actually represents:
A curie is a unit of radioactivity named after Marie and Pierre Curie. One curie represents 37 billion radioactive disintegrations per second, which is roughly the activity of one gram of radium-226. A picocurie is one trillionth of a curie, or 0.037 disintegrations per second (about 2.2 disintegrations per minute).
So when your radon test reads 4.0 pCi/L, it means that in every liter of air in your home, roughly 8.8 radon atoms are decaying every minute. That may sound tiny, but over months and years of breathing this air, the cumulative radiation exposure to lung tissue becomes significant.
3. Becquerels per Cubic Meter (Bq/m³)
The becquerel per cubic meter is the international standard unit used in most countries outside the US. It is part of the International System of Units (SI).
A becquerel is named after Henri Becquerel, who discovered radioactivity in 1896. One becquerel equals exactly one radioactive disintegration per second. The unit is simpler than the curie because it uses a base-10 relationship: 1 Bq = 1 disintegration per second.
When radon is measured in Bq/m³, it counts how many disintegrations are happening per second in each cubic meter of air. Because a cubic meter is much larger than a liter (1,000 liters = 1 cubic meter), and a becquerel is much smaller than a picocurie in terms of volume-adjusted activity, the Bq/m³ numbers are much larger than pCi/L numbers for the same radon concentration.
4. Converting Between Units
The conversion between pCi/L and Bq/m³ is straightforward:
Conversion formulas:
pCi/L to Bq/m³: Multiply by 37
Bq/m³ to pCi/L: Divide by 37
Quick reference:
1 pCi/L = 37 Bq/m³
37 Bq/m³ = 1 pCi/L
2 pCi/L = 74 Bq/m³
100 Bq/m³ = 2.7 pCi/L
4 pCi/L = 148 Bq/m³
200 Bq/m³ = 5.4 pCi/L
8 pCi/L = 296 Bq/m³
300 Bq/m³ = 8.1 pCi/L
The conversion factor of 37 comes from the relationship between the curie and becquerel (1 Ci = 3.7 x 10^10 Bq) combined with the volume conversion between liters and cubic meters (1 m³ = 1,000 L).
5. Action Levels Around the World
Different countries and organizations have set different action levels for radon. Understanding these helps put your own results in global context:
No Truly "Safe" Level
It is worth noting that no scientific organization has identified a level of radon below which there is zero risk. The EPA's 4.0 pCi/L action level is a practical threshold based on cost-effectiveness of mitigation, not a safety guarantee. Lower is always better with radon exposure.
6. Interpreting Your Results
When you receive your radon test results, here is how to interpret them:
Below 2.0 pCi/L (74 Bq/m³)
Low risk. No immediate action needed. Retest every 2 years to monitor for changes. This is a good result.
2.0 to 4.0 pCi/L (74 to 148 Bq/m³)
Moderate levels. The EPA suggests considering mitigation in this range. A long-term follow-up test can help determine if levels are consistently in this range. The WHO would recommend action above 2.7 pCi/L.
Above 4.0 pCi/L (148 Bq/m³)
The EPA recommends radon mitigation services. Above 8.0 pCi/L (296 Bq/m³), act promptly. A mitigation system typically reduces levels by 90-99%.
The Key Takeaway
Whether your result is in pCi/L or Bq/m³, the important thing is knowing how it compares to action levels. In the US, 4.0 pCi/L (148 Bq/m³) is the threshold for recommended action. If your level exceeds this, mitigation is effective and affordable. Need help understanding your report? See our guide on how to read radon test results. For an overview of available testing devices, check our radon test kit types comparison.
